Carbon dioxide and its concentration in the atmosphere is at the centre of climate change theory and policy.

The scientific consensus is that we must limit the release of carbon dioxide and similar greenhouse gases if we are going to lessen our effect on the climate. What isn't clear is how much carbon dioxide will cause runaway change.

The UK's Department for Environment, Farming and Rural Affairs gives the figure of 450 ppm as having a "medium" likelihood of avoiding a rise above 2C. More recent calculations are not so optimistic with many citing 350 parts per million (ppm) as the concentration that, if we stay above it, climate change becomes out of our hands.

The data below shows concentrations of carbon dioxide rose above 350ppm in 1998. While current levels are at 385ppm, a simple extrapolation suggests that the 450ppm level will be breached in around 2050. With energy use rising in much of the developed world the date may be much sooner. Some scientists are already arguing that 450ppm is an unrealistic target.

Our main weapons in the battle against global warming include energy efficiency, carbon capture and renewable energy technologies. An arsenal which may have to be bolstered in the years to come.